Stereotypies:

"[The] development of stereotypies indicates that well-being has probably been poor, with the animal motivated to show a behaviour pattern that it could not perform normally or to completion."

C.J. Mason 

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"Stereotypies often develop in situations of low stimulus input, physical restraint, and inescapable fear or frustration. These are situations that behavioural and physiological data indicate to be aversive and stressful. Indeed, a behavioural sign of aversion or internal conflict, such as an attempt to escape or a displacement activity, is sometimes the very source from which a stereotypy develops. Furthermore, once well established, stereotypies are often elicited on exposure to a stressor, or to barren conditions."

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"Established stereotypies are also commonly performed when little is happening in the environment, and arousal is probably low. This is true, for example, of flying to and fro incaged birds (Hinde 1962), finger-sucking and other stereotypies in children (Levy 1944; Berkson 1967) and rocking in laboratory-caged chimpanzees (Berkson 1967)."

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"Like a scar, a stereotypy tells us something about past events. It suggests that previously, a behaviour pattern has been repeatedly elicited, and probably in an environment that has demanded little variation in performance. In captivity, sustained repetition may occur because the behaviour cannot reach a satisfactory, consummatory conclusion, and in barren conditions the behaviour is unlikely to be interrupted by higher priority behaviour patterns. Thus stereotypies should warn us that the animal has probably been in an unchanging and frustrating environment, and that its welfare has probably been unsatisfactory. Much evidence does indeed link the development of stereotypies with specific sub-optimal environments. The development of a stereotypy in an individual is therefore the sign of an animal that has probably been suffering, and whose well-being may be poor still."